1. Field of the Invention
The present invention relates to a conductive polymer solution containing a π-conjugated conductive polymer, and a method for producing the same.
Also, the present invention relates to an antistatic coating material which forms an antistatic coating film. Furthermore, the present invention relates to an antistatic hard coat layer, and an optical filter.
Furthermore, the present invention relates to a conductive polymer solution containing a π-conjugated conductive polymer, and a conductive coating film.
Furthermore, the present invention relates to an antistatic tacky adhesive having antistatic properties and adhesiveness, and an antistatic tacky adhesive layer. Furthermore, the present invention relates to a protective material such as protective tape, protective sheet or protective film.
2. Description of the Related Art
Conductive materials prepared by adding (doping) an electron donating compound or an electron accepting compound (dopant) to a π-conjugated conductive polymer such as polypyrrole, polythiophene, polyacetylene, polyparaphenylene or polyaniline have recently been developed and their use is increasing.
Generally, a π-conjugated conductive polymer, in which a main chain is composed of a π-conjugated system containing π electrons, is synthesized by an electrolytic polymerization method and a chemical oxidative polymerization method.
In the electrolytic polymerization method, a substrate formed previously of an electrode material is dipped in a solution mixture of an electrolyte serving as a dopant and a precursor monomer, which forms a π-conjugated conductive polymer, to form a π-conjugated conductive polymer in the form of a film on the substrate. Therefore, it is difficult to produce a large amount of the π-conjugated conductive polymer.
In the chemical oxidative polymerization method, there is not such a restriction and a large amount of the π-conjugated conductive polymer can be prepared in a solution by adding an oxidizing agent and an oxidative polymerization catalyst to a precursor monomer of a π-conjugated conductive polymer.
However, in the chemical oxidative polymerization method, with the growth of the conjugated system of the π-conjugated conductive polymer main chain, solubility in solvent becomes inferior, and therefore the π-conjugated conductive polymer is obtained in the form of an insoluble solid powder. In case of the insoluble solid powder, it becomes difficult to uniformly form a π-conjugated conductive polymer membrane on the surface of the substrate.
Therefore, there have been made a trial of a method of solubilizing a π-conjugated conductive polymer by introducing a functional group, a method of solubilizing by dispersing in a binder resin, and a method of solubilizing by adding an anion group-containing polymer acid.
For example, there is proposed a method of preparing an aqueous poly(3,4-dialkoxythiophene) solution by chemical oxidative polymerization of 3,4-dialkoxythiophene using an oxidizing agent in the presence of polystyrenesulfonic acid as an anion group-containing polymer acid having a molecular weight within a range from 2000 to 500000 so as to improve dispersibility in water (see, for example, Japanese Patent No. 2,636,968). There is also proposed a method of preparing an aqueous colloidal π-conjugated conductive polymer solution by chemical oxidative polymerization in the presence of polyacrylic acid (see, for example, Japanese Unexamined Patent Application, First Publication No. Hei 7-165892).
Generally, the surface of an optical filter or an optical information recording medium is provided with a hard coat layer so as to prevent scratching. In these optical applications, not only high hardness but also excellent transparency and antistatic properties for prevention of adhesion of dusts due to static electricity are required to the hard coat layer.
With respect to antistatic properties, it is required that the value of surface resistance is stable within a range from about 106 to 1010Ω (that is, stable antistatic properties).
As the hard coat layer for an optical filter or an optical information recording medium, a coating film formed by coating an antistatic coating material containing a π-conjugated conductive polymer and a hard coat component may be used.
It is known that, although the π-conjugated conductive polymer itself is insoluble, the π-conjugated conductive polymer can be converted into an aqueous solution by chemical oxidative polymerization of a precursor monomer of the π-conjugated conductive polymer in the presence of an anion group-containing polymer acid (see, for example, Japanese Patent No. 2,636,968). A coating film having antistatic properties can be formed by coating the aqueous solution of the π-conjugated conductive polymer. However, when water is used as a solvent, it requires a long time to form a coating film because for low drying rate. When the π-conjugated conductive polymer is water soluble, since compatibility with the hard coat component becomes inferior, a hard coat layer having sufficient performances could not be obtained.
To solve this problem, a conductive polymer composed of a polymer of β alkylpyrrole in which a long chain alkyl group is introduced into the β-position of pyrrole is described in Japanese Patent No. 3,024,867. This conductive polymer has a bulky alkyl group and is therefore soluble in a volatile organic solvent and is also excellent in compatibility with the hard coat component.
There have also been made a trial of a method of solubilizing by introducing a functional group into a π-conjugated conductive polymer, a method of solubilizing by dispersing in a binder resin, and a method of solubilizing by adding a polyanion.
As a method of forming a conductive film on a base material, for example, there is proposed a method comprising the steps of dissolving an oxidizing agent, a vinyl chloride-based copolymer, and a monomer, which forms a π-conjugated conductive polymer, in a solvent, coating the resulting coating solution onto a base material, and polymerizing the monomer while controlling an oxidation potential using a solvent to form a complex of the vinyl chloride-based copolymer and the conductive polymer (see Japanese Unexamined Patent Application, First Publication No. Hei 5-186619).
According to the purposes, excellent thermostability is sometimes required to the conductive film. There is proposed a method comprising the steps of mixing a monomer with a compound, as a dopant, having a structure similar to that of a sulfonated substance which can be used as an antioxidant, and electrolytically polymerizing the mixture for the purpose of forming a conductive film having excellent thermostability (see Japanese Patent No. 2,546,617).
To mechanically or electrically protect the surface of various components and articles and to prevent penetration of dusts or moisture into precision instruments, components, articles, and precision instruments may have hitherto been coated with a protective material such as protective tape, protective sheet or protective film upon storage, conveyance, transportation or processing.
Generally, the protective material to be used comprises a base material and a tacky adhesive layer, formed on the base material, for applying onto components or articles. By the way, static electricity is generated when the protective material is removed. Therefore, when a protective material is applied to a display, a polarizing plate and electronic components so as to protect them, damage or deterioration of function may arise. To solve such a problem, there is proposed that antistatic properties are imparted to the protective material (see, for example, Japanese Unexamined Patent Application, First Publication No. 2001-301819, Japanese Unexamined Patent Application, First Publication No. 2001-106994, Japanese Unexamined Patent Application, First Publication No. Hei 6-295016 and Japanese Unexamined Patent Application, First Publication No. Hei 9-31222). Particularly in Japanese Unexamined Patent Application, First Publication No. Hei 6-295016 and Japanese Unexamined Patent Application, First Publication No. Hei 9-31222, there is proposed that an antistatic tacky adhesive layer is formed by coating a water soluble coating solution containing a π-conjugated conductive polymer onto a base material. However, in case of the water soluble coating solution, the drying time increases and therefore it was required to replace by an organic solvent-based coating solution.
Therefore, in Japanese Unexamined Patent Application, First Publication No. 2005-126081, there is provided that an aqueous polythiophene solution is converted into an alcohol solution of polythiophene and an acrylic polymer is dispersed in the alcohol solution of polythiophene to prepare a conductive pressure-sensitive adhesive dispersed in the alcohol, and the pressure-sensitive adhesive is used as a tacky adhesive layer.
As described above, the conductive polymer solution containing a π-conjugated conductive polymer, which has hitherto been proposed, is an aqueous solution and when a coating film is formed by coating the aqueous solution, productivity of the conductive coating film was inferior because a long drying time is required. When the π-conjugated conductive polymer is water soluble, its use was limited because of poor compatibility with the hydrophobic resin such as hard coat resin.
Under these circumstances, the present invention has been made and an object thereof is to provide a conductive polymer solution which can decrease the drying time required to form a coating film and is excellent in compatibility between the π-conjugated conductive polymer and the hydrophobic resin, and a method for producing the same.
Since the conductive polymer described in Japanese Unexamined Patent Application, First Publication No. Hei 7-165892 has low conductivity, when it is dissolved in an organic solvent to prepare a coating material, predetermined antistatic properties could not be secured if the content of the conductive polymer does not increase. When the coating material containing a large amount of the conductive polymer is coated to form a coating film, there arises a problem that the coating film is colored and transparency deteriorates. Even in case of the conductive polymer described in Japanese Unexamined Patent Application, First Publication No. Hei 7-165892, it is insufficient in compatibility with various hard coat resins each having different polarity and also a special monomer such as β-alkylpyrrole is very expensive and is not suited for practical use.
Under these circumstances, the present invention has been made and an object thereof is to provide an antistatic coating material which secures compatibility between the π-conjugated conductive polymer and the hard coat component and can form a coating film having both antistatic properties and transparency. Another object is to provide a hard coat layer which has high hardness and also has both antistatic properties and transparency. Still another object is to provide an optical filter which has high hardness and comprises a hard coat layer having both antistatic properties and transparency.
In the meted described in Japanese Unexamined Patent Application, First Publication No. Hei 5-186619, since the solvent is limited according to the kind of the base material, the polymerization of the monomer due to control of an oxidation potential is limited and therefore high conductivity can not be secured. Since the vinyl chloride-based copolymer as an insulating resin is contained, high conductivity can be secured.
In the method described in Japanese Patent No. 2,636,968, a large amount of the polyanion is contained so as to improve water dispersibility of the π-conjugated conductive polymer. Therefore, there was a problem that high conductivity is hardly obtained. Accordingly, a conductive polymer solution having both excellent conductivity and solvent solubility is required.
In the method described in Japanese Patent No. 2,546,617, there was a problem that the resulting coating film has thermostability, but solvent solubility can not be secured.
Under these circumstances, the present invention has been made and an object thereof is to provide a conductive polymer solution which is excellent in both conductivity and solvent solubility. Another object is to provide a conductive polymer solution which can enhance thermostability of the coating film. Still another object is to provide a conductive coating film which is excellent in conductivity. A further object is to provide a conductive coating film which is also excellent in thermostability.
In the tacky adhesive described in Japanese Unexamined Patent Application, First Publication No. 2005-126081, an organic solvent other than an alcohol can not be used and also an acrylic polymer as a tacky adhesive component was limited. In the tacky adhesive described in Japanese Unexamined Patent Application, First Publication No. 2005-126081, although pot life upon coating is secured, storage stability is not sufficiently excellent and it was difficult to store for only several days. For example, when several days have passed after preparation, the π-conjugated conductive polymer is aggregated and separated, and thus transparency and conductivity of the tacky adhesive layer may deteriorate.
Under these circumstances, the present invention was made and an object thereof is to provide an antistatic tacky adhesive in which a liquid organic compound other than an alcohol can be used as a solvent and the acrylic polymer is not limited and also storage stability is excellent. Another object is to provide an antistatic tacky adhesive layer which is excellent in transparency and antistatic properties, and a protective material.